Separation column

ABSTRACT

In the field of substance separation which uses the flow of a fluid, it is necessary to reduce the inside diameter of a separation column in order to meet the tendency to reduce the volume of an organic solvent used. The smaller the volume of a target sample which is caused to flow, the higher the concentration of the target sample, thereby permitting a high-sensitivity analysis. For this purpose, it is necessary to reduce the diameter of a separation column. Therefore, the manufacturing of such a separation column is difficult and besides the separation column becomes apt to fracture. Therefore, the separation column is fabricated as a double-wall tube constituted by an outer tube and an inner tube in such a manner that the outer tube is separated so as to be freely inserted and extracted. Furthermore, a union is fitted to the end of the outer tube by use of a screw thereby to prevent torsions between the outer tube and the inner tube and strains and, at the same time, to eliminate a space for a dead volume.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a separation column and, moreparticularly, to an analytical column and a separation column used inliquid phase extraction and pretreatment.

2. Description of the Related Art

In a chromatographic column for separating substances by using a fluid,the volume of the fluid which fills the interior of the column willdecrease with decreasing inside diameter of the column in proportion tothe square of the inside diameter. A fluid used in a chromatographiccolumn contains mainly an organic solvent. Therefore, it is necessary tomake efforts to reduce the volume of the fluid from the problem of theglobal environment and the like, and there is a tendency to minimize thevolume of the fluid. For this purpose, reducing the inside diameter isthe most effective means.

On the other hand, in the analysis field where chromatographic columnsare mainly used, the material for a contact portion of a chromatographiccolumn has also a great effect. In fluid chromatography, a target sampleis detected in an eluent which is caused to flow through achromatographic column and, therefore, the smaller the volume of thefluid which is caused to flow, the higher the concentration of thetarget sample, there by permitting a high-sensitivity analysis. Forreasons as described above, small chromatographic columns having acolumn diameter of not more than several millimeters in inside diameterare required.

However, a chromatographic column made of metal is corroded by a mobilephase used in the separation of a moving organism sample etc. Besides,in the manufacturing process of a chromatographic column made of metal,the smaller the inside diameter of the column, the more conspicuous theroughness of the surface of a wall face will tend to be. Therefore, thesmaller the column diameter, the higher the production cost and the moreexpensive the column.

On the other hand, in the case of a glass column, which is frequentlyused, cracks are produced from worked parts such as screws and flanges.Furthermore, a glass column has the drawbacks of low pressure stability,low resistance to high pressure and susceptibility to failure.

Therefore, there has been proposed methods by which a separation columnis fabricated separately as an outer tube and an inner tube, which arecombined into one and used. For example, the Japanese Patent Laid-OpenNo. 9-119924 describes a structure in which special steel is used as thematerial for an inner tube, which is elongated so that the insidediameter can be varied while keeping the quality of the inner surface inorder to ensure the smoothness of the inner surface and this inner tubeis held within a carrier tube, which is an outer pipe, by use of anadapter member. Furthermore, in the Japanese Patent No. 2619273 isproposed a structure in which a glass tube is inserted in an outerjacket and a column is formed by use of a plunger and union nutsincluding a milled nut, which are column connection members. In bothcases, a double structure is adopted in which a small-diameter tube isobtained by the precision and ease of manufacture of the inner tube andthe weakness of the inner tube is protected by the outer tube.

In the above Japanese Patent Laid-Open No. 9-119924, however, for theconnection to a chromatographic apparatus, it is possible to performconnection to a cartridge system through a groove 24 by use ofconventional connection parts. The connection design is such that,first, by use of a support nut fitted into a tube of a separationcolumn, part of the tube is fitted into the groove 24 which forms thegroove of the tube, a strass member which is a connection part is fittedinto a tube end and the support nut is screwed together by a cap nut,thereby to support and fix the strass member (the U.S. Pat. No.4,737,284). Therefore, the number of parts is large and a simpleconnection is not obtained.

In the latter patent, the connection to a chromatographic apparatus etc.is such that with the inner tube inserted in the outer tube, a plungerprovided with a discharge line is inserted into an end of the glasstube, which is the inner tube, and is fixed by the union nut having themilled nut. Therefore, it is necessary that the plunger etc. enter theend of the glass tube, which is the inner tube, and hence it isdifficult to make an inner tube having a small diameter. Furthermore,when only the pipe end is formed wide, this provides the drawbacks of adifficulty in manufacturing, inconvenience of use, susceptibility tocracking, etc. Moreover, when the separation column is connected to achromatographic apparatus etc., a system which involves screwing themilled nut and the union nut into is adopted, and in fixing both ends ofthe separation column, torsions and strains may sometimes be given tothe inner tube. In this case, the smaller the diameter of the innertube, the more an adverse effect on the rheological properties of asample substance will apt to be produced.

Also, when Teflon (registered trade name), which has no pressureresistance, etc. are used in the inner tube, this provided the fear of afracture due to liquid pressure. Furthermore, in chromatography, thelower the temperature, the lower the moving speed of sample componentswithin the column, with the result that elution can be delayed. When thetemperature is further lowered, the sample components accumulate at theinlet of the column and can be concentrated. In this state, the samplecomponents which do not elute cannot be detected. Therefore, there hasbeen no effective means although it is possible to cause a targetcomponent to be eluted by raising the temperature after the targetcomponent is concentrated at the inlet of the column.

Therefore, in the present invention, there is proposed a separationcolumn, which is formed as a double-wall tube comprising an inner tubeand an outer tube, permits easy connection to a chromatographicapparatus etc. owing to its very simple structure, and provides acomplete gastight construction so that during the connection and fixingof the separation column torsions and strains between the outer tube andthe inner tube are prevented, thereby eliminating an adverse effect of adead volume etc. on the inner tube.

SUMMARY OF THE INVENTION

In the present invention, there is provided a separation column which isformed as a double-wall tube, comprising: an inner pipe; an outer pipe;and a union nut, the union nut being freely screwed to an end of theouter pipe; the outer pipe being divided so as to be freely inserted andextracted. As a result of this, when the separation column is formed byscrewing in the union nut, the fixing of the position of the inner tubeis performed by the union nut and, therefore, the torque of the unionnut is transmitted to the inner tube and there is a possibility that theinner tube is twisted or strains are given to the inner tube. At thistime, however, by shifting the fitting of the outer tube to make anadjustment, the torque of the union nut can be prevented from beingtransmitted to the inner tube. Or alternatively, the torque of the unionnut can be corrected.

As a result of this, it is possible to completely ensure the performanceof the separation tube without causing any damage to the performance ofthe separation column and the analysis capacity can be ensured.Furthermore, there is no space for a dead volume and it is possible topositively prevent a dead volume. Needless to say, the precision workingof the inner tube is possible owing to the inner and outer double-wallstructure. Besides, the construction of the outer tube is simple and thenumber of parts is small for the whole separation column. Hence, theseparation tube provides convenience in use and is easy to use andadvantageous in terms of cost.

In the present invention, in the above-described separation column, theunion nut is screwed into the outer tube and the outer tube is fixed viaa ferrule. As a result of this, the inner tube is held in a fixedposition by means of the ferrule and firmly fixed without the need touse other parts simply by screwing in the unit nut.

Furthermore, in the present invention, in the above-described separationcolumn, the outer tube has one or more holes or connection parts whichcommunicate with a space between the inner tube and the outer tube. As aresult of this, it becomes possible to reduce a pressure differencebetween the outer tube and the inner tube by putting a fluid between theouter tube and the inner tube in order to resist the liquid pressure inthe inner tube, it becomes possible to cause a target componentconcentrated at the inlet of the column to be eluted by raising thetemperature, and by bringing the inner tube into contact with theoutside air or another fluid etc., it becomes possible to easily performvarious operations such as temperature regulation and pressureregulation. This is effective in protecting the inner tube andshortening the analysis time.

Furthermore, in the present invention, in the above-described separationtube, at least part of the union nut is formed by a transparentmaterial. As a result of this, this formed transparent part enables thefixing of the inner tube in position to be visually recognized and thetightening condition when the ferrule is used can be checked. Thus,operations can be perfectly carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a separation column takenalong the centerline thereof in an embodiment of the present invention;

FIG. 2 is a longitudinal sectional explanatory diagram of a separationcolumn taken along the centerline thereof in an embodiment of thepresent invention;

FIG. 3 is a longitudinal sectional explanatory diagram of a separationcolumn taken along the centerline thereof in an embodiment of thepresent invention;

FIG. 4 is a longitudinal sectional explanatory diagram of a separationcolumn taken along the centerline thereof in an embodiment of thepresent invention;

FIG. 5 is a longitudinal sectional explanatory diagram of a separationcolumn taken along the centerline thereof in an embodiment of thepresent invention;

FIG. 6 is a partially enlarged explanatory diagram of FIG. 1;

FIG. 7 is a diagram to explain the use condition of an embodiment of thepresent invention;

FIG. 8 is a chromatogram diagram obtained by use of a conventionalcolumn;

FIG. 9 is a chromatogram diagram obtained by use of a column of thepresent invention;

FIG. 10 is a chromatogram diagram obtained by use of a column of thepresent invention;

FIG. 11 is a chromatogram diagram obtained by use of a conventionalcolumn;

FIG. 12 is a chromatogram diagram obtained by an implementationexperiment in Embodiment 3 of the present invention; and

FIG. 13 is a longitudinal sectional explanatory diagram of a separationcolumn taken along the centerline thereof in an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail on the basis of theembodiments shown in the drawings.

The separation column in the present invention includes a capillarycolumn, including a microcolumn, a general-purpose analytical column, aguard column, a preparative column, a solid phase extraction column andother pretreatment separation columns.

In the figures, the numeral 1 denotes an inner tube, and it is commonpractice to use a fine tube such as a micro capillary column, forexample, a capillary column made of fused silica. Although the materialfor the inner tube 1 is not especially limited, the inner tube 1 isformed from a desired material, such as synthetic resins of PEEK etc.,stainless steel and stainless steel the inner surface of which is linedwith glass. It is preferred that the ends of the inner tube 1 be eachprovided with a ferrule 5.

The numeral 2 denotes an outer tube, which is divided into two members21, 22. An engaging convexity 211 is formed in one member 21 and anengaging concavity 221 is formed in the other member 22. Although theengaging convexity 211 and the engaging concavity 221 are each formed ina stepped manner, it is also possible to form them in a tapered manner.The outer tube 2 can be formed from a desired material, such assynthetic resins of PEEK etc., stainless steel and stainless steel theinner surface of which is lined with glass. Union nuts 3, 3 are screwedinto both ends of each member 21, 22 of the outer pipe 2. A through hole31 is provided in the union nut 3 and a convexity 32 is provided in themiddle part of the through hole. A fine pore 321 is formed in the middleof this convexity 32. (FIG. 6)

The numeral 4 denotes a filter the circumference of which is surroundedby a packing 41, and in this state the filter 4 is inserted in thethrough hole 31 of the union nut 3 and caused to abut against theconvexity 32. Although it is convenient to use a SUS sintered filter anda SUS screen filter as the filter 4, other filters may also be used.This filter is effective in preventing a filler from flowing out andentering the fine pore 1 or dust and crystals from flowing in. It isrecommendable that the outer tube 2 be provided with a joining partadaptable to a commercially available cartridge system, for example,locking grooves 6, 6 suited to the joint portion of the U.S. Pat. No.4,737,284. In this case, it is also possible that the union nut 3 isscrewed into a screw groove provided in the outer tube 2 and thatanother support nut locked in the above-described locking groove 6.Furthermore, this locking groove 6 can also be used as a locking portionfor a rotary mechanism formed by drilling part of a round tube.

Needless to say, length and inside diameter settings of the outer tube 2can be freely selected depending on the purpose and an object to beseparated. However, in the setting of the length, for example, it isalso possible to perform setting in such a manner that one outer tube 21is used as the basis and a selection is made from different lengths ofthe other outer pipe 22 (FIG. 3). Furthermore, the outer pipe 2maybedivided into three members 21, 22, 23 and it is possible to use themembers 21 and 22 as the basis and set the length of the middle member23 at a long value (FIG. 4). Also, a bent tube may be used as the member23 (FIG. 5).

It is possible to provide a hole portion 25 in the outer tube 2, therebybringing the outside air into contact with the space between the innertube 1 and the outer tube 2. As a result of this, it becomes easy toadjust the temperature of the inner tube 1 to the outside airtemperature. It is also possible to provide a cover 27 which can openand close. Also, by introducing a temperature-regulated liquid and gasfrom this hole portion 25, it becomes possible to adjust the temperatureof the inner tube 1 and temperature raising, cooling, etc. can beperformed in a shorter time, with the result that this arrangement canbe used in shortening the analysis time and performing concentration. Itis possible to provide a connection member 28 of other tube etc. in thishole portion 25. Also, it is possible to provide an appropriate numberof hole portions 25 in the outer tube 25 and, therefore, variousoperations are possible; for example, a liquid is caused to circulatebetween two hole portions 25, 25 and the liquid is extracted fromanother hole portion 25, or different temperature-regulating media areintroduced from two places and discharged from one hole portion 25 (FIG.7, FIG. 13).

When Teflon (registered trade name), which has no pressure resistance,etc. are used in the inner tube 1, by applying a liquid pressure fromthis hole portion 25, it is also possible to use this hole portion 25 inpreventing a breakdown of the inner tube 1. For example, by filling theouter tube with water at 10 MPa in a low pressure mode by use of a highpressure pump, the inner column made of Teflon (registered trade name)can be used without a breakdown because a pressure difference does notoccur up to 10 MPa. Furthermore, if a transmitting resin suited for thepurpose is used as the material for the inner tube 1, the presentseparation column can be used in demineralization etc. by causing waterto flow through the outer pipe. For example, a tube through which onlyNa ions are caused to pass is filled with an anion exchange filler andis used as the inner tube column. When a sample containing a largeamount of salt is injected, with water kept flowing through the outertube, it is possible to remove the Na ions by the ion exchange capacityof the tube.

The accumulation of Na ions into ananion exchange filler filled in theinterior does not occur and the life is substantially extended. Thiseffect applies also to a reversed phase column etc. and the protectionof a filler filled in the interior and the cleanup effect of ion removalare ensured. Furthermore, by using a tube that performs selectivetransmission by the molecular weight, it is possible to discharge agiven amount of components from inside a column to the outside, the sameprotection of an inner column and cleanup effect as described above canbe obtained.

EXAMPLES Example 1

A microcapillary column 1 as an inner tube which is selected accordingto the purpose is inserted into an outer tube 2. At this time, both endsof the microcapillary column 1 have portions exposed from the outer tube2. Ferrules 5, 5 are fitted into both ends beforehand. Next, union nuts3, 3 are put on both ends of the outer tube 2 and screwed in. At thistime, both ends of the microcapillary column 1 are inserted into athrough hole 31 of the union nuts 3, 3 and the leading end of themicrocapillary column 1 is brought into contact with a filter 4. As theunion nuts 3, 3 are crewed in, the ferrule 5 is caused to abut against ataper 311 formed in the through hole 31 and tightens this taper, therebyforming a separation column 7. (FIG. 1, FIG. 6)

FIG. 9 shows a chromatogram obtained by conducting an experiment usingEmbodiment 1 under the following conditions.

A microcapillary column having an inside diameter of 0.3 mm, inparticular, lacks physical endurance and is apt to be broken. Peakbreaking is observed as shown in FIG. 8 in a column obtained by fillinga PEEK tube 0.3 mm in inside diameter and 150 mm in length with Inertsil(registered trade name) ODS-33 μm at a high pressure was given aphysical force and bent. When the column of the present invention wasused, the inner tube was protected by the outer tube and was not bentand the chromatogram of FIG. 9 was obtained. In the chromatogram of thepresent invention, the effect on the protection of the inner tubedisplays itself.

Analysis Conditions

-   -   Eluent: 65% acetonitrile    -   Flow rate: 4 μl/min    -   Detection wavelength: UV 254 nm    -   Sample volume: 10 nl    -   Column temperature: Room temperature

Sample Components

-   -   1 Acetophenone 2 Benzene 3 Toluene 4 Naphthalene

Example 2

Example of application to an analysis of benzpyrene in the environmentalwater

A column the outer tube 2 of which has three hole portions 26, 26, 26 isused. A drain pipe 28 is connected to one of the hole portions 26 and islocked by a pinch cock. The remaining two hole portions 26, 26 areconnected to a circulating constant-temperature water tank 29 by use ofconnection parts 28, 28 and methanol at 4° C. is circulated. Thetemperature of the whole column is regulated by use of a column oven at7° C. The temperature in the interior of the column reaches temperatureequilibrium, though this depends on the flow rate of the circulatingconstant-temperature water tank and the inner tube diameter, and thetemperature of the inner tube is controlled to 4° C. When a sample isintroduced at 4° C., the matrix components other than the targetbenzpyrene are eluted first. In 2 minutes after the approach of thematrix components to the outlet, the circulation in the circulatingconstant-temperature water tank is stopped and simultaneously the liquidin the tank is extracted by means of the drain pipe. As a result ofthis, the temperature is abruptly raised to a setting of the column ovenof 70° C. Benzpyrene is separated from the matrix in a shorter time andis eluted. FIG. 8 shows a chromatogram obtained by the embodiment shownin FIG. 7.

It is possible to make provisions for the next injection by recoveringthe initial conditions after the elution of benzpyrene. It is alsopossible to automate these series of operations by connecting solenoidvalves etc. to the line and by synchronizing the operations withinjection.

FIG. 11 shows an example of an analysis of benzpyrene in theenvironmental water at a constant temperature of 50° C. In this case, itis impossible to obtain quantitativeness due to the presence ofbenzpyrene on the environmental water matrix. When a column of thepresent invention is used, however, the matrix and benzpyrene arecompletely separated, permitting quantitative determination. (FIG. 10)

In a case where a column oven is not used and liquid carbon dioxide iscaused to flow in the initial period to perform cooling and hot water at70° C. is caused to flow, a similar effect is obtained. In fact, thesame effect as in FIG. 10 was obtained. In this case, the effect isgreat when the injection side is provided in the lower part, hot wateris put and the drain is set in the upper part, and it is also possibleto give a temperature gradient to the inlet and outlet of the column

Analysis Conditions

-   -   Chromatogram (FIG. 10)

Filling of a column of the invention 0.5 mm in inside diameter and 150mm in length with Inertsil (registered trade name) ODS-P 5 μm

-   -   Eluent: 80% acetonitrile Flow rate: 20 μl/min    -   Detection wavelength: UV 254 nm    -   Volume of injected sample: 10 μl    -   Sample: Addition of 10 ppm of benzpyrene to drain    -   Temperature control (refer to the description.)    -   Chromatogram (FIG. 11)    -   Filling of a conventional column with Inertsil (registered trade        name) ODS-P 5 μm    -   Eluent: 80% acetonitrile Flow rate: 20 μl/min    -   Detection wavelength: UV 254 nm    -   Volume of injected sample: 10 μl    -   Sample: Addition of 10 ppm of benzpyrene to drain    -   Temperature: 50° C. constant

Example 3

It is not always necessary that a separation column of the presentinvention is a straight tube, and the invention can also be applied tobent tubes such as a U-shaped tube.

This separation column can be used in a case where the separation columnis connected directly to an injector loop of liquid chromatography and asolid phase is extracted and in pretreatment for the trapping of theair. In an integrated protective tube, it is impossible to ensure theaccuracy of a connection part of a union nut 3 and the fabrication isdifficult. In this system of the invention, bent tube portions andstraight tube portions can be fabricated as separate parts and,therefore, the accuracy of the connection parts can be increased.

When a straight tube is to be attached to a loop portion of an injector,piping for connection is required; hence parts such as joints and pipingare necessary and labor is also required. Furthermore, because theinterior of the piping is not filled with a filler, a dead volume isproduced and the peak shape worsens. The column of the present inventioncan be applied to a bent tube and can be attached directly to theinjector and the loop portion.

Furthermore, in the case of a U-shaped tube, the whole column can beeasily immersed in a cooling medium such as liquid nitrogen and only atarget component can also be concentrated and trapped.

Because separate parts are used, it is possible to fabricate variousshapes of column by combining bent tubes and straight tubes, and bychanging combinations it is possible to design the column shapeaccording to the purpose, for example, immersing only the U-shapedportion in a cooling medium and keeping the temperature of the remainingparts at room temperature.

The following experiment was conducted by use of the separation columnof the present invention shown Example 3 and the chromatograph shown inFIG. 12 was obtained.

An isochratic HPLC system in which a column 0.5 mm in inside diameterand 150 mm in length is filled with Insertsil (registered trade name)ODS-3 3 μm was prepared. As an eluent, a mixture of acetonitrile and 60mM NaCIO 4 (40/60) adjusted to pH 2.5 with phosphoric acid was used at aflow rate of 4 μl/min. An electrochemical detector with W1=900 mV andtemperature of 33° C. was used for detection.

A bent-tube column of the present invention 0.5 mm in inside diameterand 100 mm in length, which is filled with Econoprecip ODS-40 μl, wasconnected to the injector loop portion in place of a loop. The sampleused was obtained by adding 0.1 ppb of bisphenol A to clean water.

The injector was switched to the load side and 1 ml of sample water wasinjected by use of a syringe. The target bisphenol A is concentratedwithin the column. Next, the injector was switched to the inject sideand an analysis was made. As a result, bisphenol A havingquantitativeness as shown in the chromatogram was detected. The sameconcentration column was used in analyzing the air components. Theconcentration column was immersed in liquid nitrogen and cooled and 400l of bisphenol A was added by use of an air pump and the air wasintroduced. After the switching of the injector to the load side, theconcentration column was attached to the loop portion. After that, 1 mlof pure water was injected, the injector was switched to the inject sideand an analysis was made.

As a result, a similar chromatogram was obtained. Although in thisexample a manual operation was performed, it is also possible to performthe operation automatically by using an automatic valve in place of theinjector, building solenoid valves etc. in the line, automaticallyexchanging a solvent which is caused to flow, and feeding a sampleliquid by use of a syringe pump etc.

As described above, according to a separation column of a first featureof the present invention, there is provided a double-wall tube, whichcomprises: an inner pipe; an outer pipe; and a union nut, the union nutbeing freely screwed to an end of the outer pipe; the outer pipe beingdivided so as to be freely inserted and extracted. As a result of this,when the separation column is formed by screwing in the union nut, thefixing of the position of the inner tube is performed by the union nutand, therefore, the torque of the union nut is transmitted to the innertube and there is a possibility that the inner tube is twisted orstrains are given to the inner tube. At this time, however, by shiftingthe fitting of the outer tube to make an adjustment, the torque of theunion nut can be prevented from being transmitted to the inner tube. Oralternatively, the torque of the union nut can be corrected.

As a result of this, it is possible to completely ensure the performanceof the separation tube without causing any damage to the performance ofthe separation column and the analysis capacity can be ensured.Furthermore, there is no space fora dead volume and it is possible topositively prevent a dead volume. Needless to say, the precision workingof the inner tube is possible owing to the inner and outer double-wallstructure. Besides, the construction of the outer tube is simple and thenumber of parts is small for the whole separation column. Hence, theseparation tube provides convenience in use and is easy to use andadvantageous in terms of cost.

According to a separation column of a second feature of the presentinvention, the union nut is screwed into the outer tube and the outertube is fixed via a ferrule. Therefore, the inner tube is held in afixed position by means of the ferrule and firmly fixed without the needto use other parts simply by screwing in the unit nut.

According to a separation column of a third feature of the presentinvention, the outer tube has one or more holes or connection partswhich communicate with a space between the inner tube and the outertube. Therefore, by bringing the inner tube into contact with theoutside air or another fluid etc., it becomes possible to easily performvarious operations such as temperature regulation and pressureregulation. This is effective in protecting the inner tube andshortening the analysis time.

Furthermore, according to a separation column of a fourth feature of thepresent invention, at least part of the union nut is formed by atransparent material. Therefore, this formed transparent part enablesthe fixing of the inner tube in position to be visually recognized andthe tightening condition when the ferrule is used can be checked. Thus,operations can be perfectly carried out.

1. A separation column which is formed as a double-wall tube,comprising: an inner pipe; an outer pipe; and a union nut, the union nutbeing freely screwed to an end of the outer pipe; the outer pipe beingdivided so as to be freely inserted and extracted.
 2. The separationcolumn according to claim 1, wherein the union nut is screwed into theouter tube and the outer tube is fixed via a ferrule.
 3. The separationcolumn according to claim 1 or 2, wherein the outer tube has one or moreholes or connection parts which communicate with a space between theinner tube and the outer tube.
 4. The separation column according toclaim 1 or 2, wherein at least part of the union nut is formed by atransparent material.
 5. The separation column according to claim 3,wherein at least part of the union nut is formed by a transparentmaterial.